An elevator or lift cage safety device must, in the ready position, be held in a defined position in which, with a minimum spacing relative to a guide surface of a guide rail against which the safety device bears in the activated state, no contact of either an active or a passive part of the safety device takes place. The minimum spacing relative to the guide rail is required in order to achieve a short reaction time for the safety device when triggered. For this purpose, in known embodiments a lateral abutment is provided against which the safety device is urged by means of a spring force, the safety device thus adopting a defined position of readiness. In one such embodiment the safety device can be laterally displaced against the spring force to adopt a self-centering position without exerting lateral pressure on the guide shoe.
A safety device of the aforesaid kind is disclosed in Swiss Patent No. 650 479. The safety device is mounted to be laterally displaceable and is pressed by means of a compression spring against an adjustable abutment. The play between the cage guide rail and the passive part of the safety device can be set by means of a setting or adjustment screw. The passive part of a safety device is the side of the device disposed opposite a catch roller or a catch wedge, wherein the catch roller or the catch wedge is correspondingly identified as the action part.
In the disclosed arrangement large vertical forces, which require correspondingly large frictional forces to halt the lateral displacement, arise during triggering of the safety device. A retarded horizontal displacement leads to a delayed brake engagement and to an amplified braking jolt and increases the injury risk to passengers in the lift cage.
The tripping of the safety device and its engagement with the cage guide rail or other fixed element generates an abrupt increase in the vertical retardation or braking force, which must be accepted and withstood by the cage construction. It is accordingly desirable that this steep increase in the vertical retardation forces be transmitted in a weakened or damped manner to the cage construction. European Patent Application EP 0 562 931 depicts a construction in which such results are partly accommodated. A safety device, which is rigidly mounted at its side, can move vertically upwardly against spring forces through a defined travel distance when the safety device engages. Compression springs arranged above the safety device providing such spring forces allow the vertical retardation force on the cage construction to rise linearly during braking and can thus, with optimum dimensioning, correspondingly reduce the retardation jolt. However, such optimum dimensioning of the springs cannot be made to accommodate differing degrees of cage loading, and accordingly appropriate compromises have to be made.
It is an object of the present invention to provide an improved mount for a safety device having simple construction, which is self-centering, has required horizontal displaceability and which displays gentle force transmission to the cage construction.
The invention is distinguished inter alia in that a catch housing of the safety device in the readiness position is urged vertically against a mechanically positive positioning device, whereby a defined position in the horizontal plane is achieved. The catch housing, when braking is triggered, is displaced from the readiness position, and automatically aligns with the guide rail, and allows the application of retardation forces on the cage construction. The catch housing is freely movable after the triggering.
A quasi mechanically positive positioning of the safety device in the readiness position may be achieved by means of conically pointed pins on one side and preferably conically pointed bores on the other side between the catch housing and the safety device holder.
A resilient plate may be positioned between an upper side of the catch housing and a lower side of a carrier plate. Bias exerted by the resilient plate presses and maintains the catch housing in the readiness position with the quasi mechanically positive support. During activation and braking the mechanically positive support is cancelled to allow for self-centering while simultaneously effecting a damped and sprung transmission of the retardation forces to the cage construction.
A rubber plate with matched Shore hardness is preferably provided as resilient plate. The resilient plate may be provided on its side facing the catch housing with a slide foil for eased lateral displacement during the self-centering.
Balls and spherical recesses as well as knife-edge and notch can be provided as horizontal fixing elements.
The mount, according to the invention, of the safety device is usable with both roller and wedge safety devices. The mount can be arranged below or above a lift cage.